Automated data storage libraries are known for providing cost effective access to large quantities of stored data. Generally, data storage libraries include a large number of storage slots on which are stored portable data storage media. The typical portable data storage media is a tape cartridge or an optical cartridge. One (or more) accessor typically accesses the data storage media from the storage slots and delivers the accessed media to a data storage drive for reading and/or writing data on the accessed media Suitable electronics both operate the accessor and operate the data storage drives to transmit and/or receive data from an attached on-line host computer system.
In a conventional automated data storage library, the storage slots are arranged in a planar orthogonal arrangement forming a "wall" of storage slots for holding data storage media. The plane may be a flat plane, or may be a cylindrical plane. To double the storage capacity, two "walls" of storage slots may be provided on either side of the accessor.
A number of different companies manufacture automated data storage libraries today, each model displaying various different features. One example is the IBM 3494 Data Storage Library. Some of the automated data storage libraries have dual or multiple accessors to provide a level of redundancy, in that, one accessor is the "active" accessor and the other may take over the accessor function and be the active accessor.
In many conventional libraries, one of the accessors is always the active accessor, and the other(s) is always spare. For example, in a dual accessor automated data storage library, the active accessor conducts all of the operations to access and move the data storage media, and the other accessor is the spare and is moved out of the active operation area. In other conventional libraries, the accessors may share the active operation and no accessors are spare. In some of the dual accessor libraries, for example, that described in U.S. Pat. No. 5,513,156, Hanaoka et al., both accessors are operated simultaneously by a single accessor controller, while another accessor controller is spare. The patent assumes that all accessors are constantly available.
Occasionally, an accessor may become unavailable, for example, if a component of the accessor must be replaced or repaired. In the typical library, the unavailable accessor is moved offline so that maintenance can be effected, for example, as described in Japan PUPA 4-23118. Often, it would be helpful if the unavailable accessor were exercised to diagnose the problem or to identify that the repair or replacement is correct. For example, in Japan PUPA 1-318113, the library manager or controller conducts a diagnosis program while the accessor is on-line. In such a case, the normal operation of the accessor and therefore of the library is suspended while the diagnosis is conducted.